In recent years, various types of home electric appliances (electronic devices) such as television sets, refrigerators, washing machines, air conditioners, rice cookers, and microwave ovens are used in houses. In addition to displaying picture, indicator lamps, and electronic buzzer sound, there is artificially synthesized voice or sound as means for informing a user about the operation of the home electric appliances. Thus, there are cases where sounds emitted from a plurality of home electric appliances interfere with each other. For example, there is a case where it is hard to hear sound from the television set, because of the interference of sound generated from a television set in a living room and sound generated from a cooking appliance in a kitchen for informing of the end of cooking. Further, there is a case where it is hard to hear sound from the television set, because of operating sound of home electric appliances such as wind noise generated from fans of an air conditioner, an electric fan, and an extractor fan, water splash noise generated from a dishwashing machine, and motor noise generated from a compressor motor of a refrigerator.
A microcomputer for a home electric appliance is capable of not only controlling the home electric appliance which is a host device (first device) but also implementing a communication function with a home electric appliance which is the other device (second device). There have been proposed systems for controlling the operation of the first device in conjunction with the operation of the second device by using such a communication function, such as HEMS (Home Energy Management System) which is an energy management system for a house.
Further, to prevent an interference between sounds from first and second devices arranged next to each other, there has been proposed a system in which normal volume level control is performed on the first device when only the first device is in operation and the volume levels of the first and second devices are set at predetermined low volume levels (non-interference volume levels) when both of the first and second devices are in operation (see Patent Reference 1, for example).